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Maximize Cattle and Dewormer Performance with Combination Treatment

Using two dewormers from different drug classes maximizes cattle efficiency, controls more parasites and reduces risk of resistance.

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By DL Step, DVM, Boehringer Ingelheim

If you’re looking to boost cattle performance and productivity, using two dewormers from different drug classes can be a great option for your herd. By working with your veterinarian to administer parasiticides from different drug classes, you maximize efficacy and control more parasites — reducing the risk of developing parasite resistance in your herd.

Known as combination treatment, the practice has been proven to reduce fecal egg counts in cattle herds by nearly 99%.1 When high efficacy like this is achieved in controlling parasites, there are fewer resistant parasite survivors to cause trouble down the road.

How does combination treatment work?

All commercially available dewormers kill parasites. Where they differ is the persistence of activity and ability to control target parasites.

Commonly used cattle dewormers can generally be divided into two different classes depending on their chemical structure. Successful combination treatment requires using one dewormer from each:

  1. Macrocyclic lactones (endectocides) come in injectable and pour-on formulations. The active ingredients cause nerve paralysis of internal and external parasites. Macrocyclic lactones provide longer-duration control of parasites compared to benzimidazoles.

  2. Benzimidazoles (white dewormers) are administered orally and act as a purge to internal parasites. These dewormers interfere with the microtubules of the parasites, which depletes the energy supply and causes death of the parasite. Benzimidazole dewormers are usually in and out of the system within a couple of days.

It’s important to remember that there are multiple active ingredients within each class of dewormers, all of which use the same mode of action to eliminate parasites.

Incorporate These Practices

In addition to implementing combination treatment, there are other ways that cattle producers can maximize dewormer efficacy for years to come:

  • Product selection. While the active ingredient may be the same, there can be many differences in how dewormers are manufactured, the quality measures taken, and even other ingredients included. And there can be quite a difference in how some generic products perform.2 Be sure to choose products backed by extensive research.

  • Product application. It’s difficult to know for sure if a dewormer is doing its job if it’s not administered correctly. Be certain the product is stored correctly, the dose you’re administering is accurate for the weight of animal you’re treating, and your equipment is properly functioning prior to treating animals.

  • Diagnostic testing. Performing routine diagnostic tests such as fecal egg counts and coprocultures can help you assess the effectiveness of your deworming program.

  • Refugia. Refugia, where a small percentage of the herd is intentionally not dewormed, is recognized as the single most important factor in delaying the onset of parasite resistance. Leaving a portion of the parasite population in “refuge” from dewormers reduces drug-resistance selection pressure caused by the dewormer. 

  • Pasture management. Limit overgrazing, maintain appropriate forage height and rotate pastures if possible.

  • Cattle management. Producers can increase overall herd immunity through routine vaccinations and enhanced nutrition. In addition, implementing biosecurity measures can help prevent the introduction of resistant parasites into the herd. 

Correct dosing, choosing the right animals to deworm and parasite monitoring will benefit your cattle and the industry's future. Be sure to consult a local veterinarian when evaluating or adjusting your deworming program.  


Paras K, Georgia M, Howell S, et al. Prevalence of gastrointestinal nematode resistance to ivermectin anthelmintics on beef cattle operations in Georgia. In Proceedings: 2017 AABP Annual Conference: 201.

2 Yazwinski TA, Tucker CA, Hornsby JA, et al. A field trial evaluation of several commercial ivermectin pour-on products in cattle. Arkansas Cattle Business, 20(9), 44-46. 2004.

©2021 Boehringer Ingelheim Animal Health USA Inc., Duluth, GA. All Rights Reserved. US-BOV-0208-2021-A



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